Grounding Sub Panel

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  #1  
Old 10-02-05, 05:09 PM
dichroic
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Grounding Sub Panel

Hope this forum can help me. I hear lots of conflicting information about my concerns.
I am installing a subpanel 550 feet away from my main panel. There are three wires, two black and one white. There is no grounding wire. I have been told by two electricians that if I ground the subpanel, with a gound rod, I don't need to run a ground wire between both boxes. The subpanel will not be bonded between the neutral and ground.
The two black wires will come from a breaker in the main panel and the white will come from the neutral in the main panel. The two blacks will go to the 100 amp breaker in the subpanel and the white to the neutral. I will ground the subpanel with a ground rod. There is no ground wire coming from the main panel to the subpanel. The bonding strap will be removed in the subpanel. The conduit is pvc, not a metallic pipe. There are no phone lines or waterpipes in the area. Is this a correct way to do this or is it necessary to run a ground between the two?
thanks for any help you can give me.
donald
 
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  #2  
Old 10-02-05, 05:53 PM
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If there is no other metallic path between the buildings (i.e., no phone line, no gas pipe, no water pipe, no coax cable, no nothing), then you can skip the grounding wire between the buildings. The neutral and grounding then absolutely must be bonded in the subpanel.

Yes, you need a grounding rod. But that would be true whether or not you ran a grounding wire between buildings. The grounding rod and grounding wire serve different purposes.

550 feet is a very long way. Be sure to do a voltage drop calculation.
 
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Old 10-02-05, 06:13 PM
dichroic
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John,
Thanks for getting back so quickly. This concern is driving me crazy. I'm going to assume that there must be a water pipe somewhere buried near my house. There also is a coaxial cable in the ground, but it is in a plastic coating, not exposed to ground. I can safely say that the cable I have buried in PVC that goes to my subpanel goes nowhere near a water pipe. The water pipes are in the front of the house, and the PVC is at the back of the house. Will this be acceptable to not running a ground between the two panels. If I have to put in a ground, I have to remove the 550 of wire from the PVC and re-pull it with a copper ground. I'm just trying not to do this, BUT, I want to do it correctly. That's the most important.
The wire size I am using was calculated by my local power company and it is very large, so shouldn't have too much voltage drop. They are the ones that actually told me I didn't need to run a ground wire between the two panels, as did the electrical company I purchased the wire. But in what I'm reading, I'm not so sure.
I certainly appreciate your help.
donald
 
  #4  
Old 10-02-05, 06:38 PM
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Originally Posted by dichroic
Will this be acceptable to not running a ground between the two panels.

If a water pipe or a coax line runs between the building where the main panel is located and the building where this new panel will be located then you need to add the ground wire.

You should anyway, as you never know what you may want to add in the future.
 
  #5  
Old 10-03-05, 06:51 AM
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It doesn't matter what is near what, or whether or not the coating is plastic, or whether or not the wire is exposed. It only matters whether or not there is anything metalic that runs from one building to the other.
 
  #6  
Old 10-03-05, 08:10 AM
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The relevant NEC Article----------

250.32, (separate) structure supplied by a Feeder , (2) Grounded ( Neutral) Conductor

"(1), Where an Equiptment Grounding Conductor is not run with ( the Feeder Conductors) to the seperate structure and (2), THERE ARE NO CONTINUOUS METALLIC Paths (between the Grounding Electodes ) in each structure, the (Feeder) Grounded Conductor shall be connected to the Grounding Electrode ( at the seperate structure) , and shall be used for Grounding and Bonding ( at the seperate structure )"
 
  #7  
Old 10-03-05, 07:44 PM
dichroic
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Thanks for all the input....
I'm going to pull all the wire out of the PVC conduit and pull a ground wire, so now I have 4. The box will not be bonded, but I will put in a grounding rod. Hopefully this will solve my dilema.
donald
 
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